The prior art teaches the manufacture of pressure sensitive adhesive (PSA) compositions by solution and emulsion polymerizations. PSA produced by solution polymerization may be diluted with a solvent and coated in a thin layer on a backing material by processes well known in the adhesives art. In coating articles such as tapes with solution polymer PSAs, elaborate drying ovens have been required to carry away the volatile solvents after coating. Furthermore, to prevent the solvents from being vented to the atmosphere with resulting pollution and solvent loss, expensive solvent recovery equipment has been required. Safety hazards in such operations are also severe, as the solvents are flammable and precautions must be taken to avoid explosive mixtures in the oven and exhaust systems.
While emulsion polymerization has potentially eliminated the problems associated with handling and evaporation of flammable solvents (e.g., when adhesive is applied as a latex to a tape backing) the heat of vaporization of water must be supplied to dry the coating, and essentially the same drying equipment as used in solution coating must be employed. Direct coating of latices can give a coating with increased moisture sensitivity due to residual emulsifiers, and there are backings and substrates which are sensitive to moisture. Latex requires a higher drying temperature than solution polymers, and latex can lack stability in storage and handling, forming coagulum and plugging equipment.
Currently, glass bubble filled acrylate adhesive is sold as a positionable mounting adhesive. A positionable PSA should meet the following criteria:
(a) The adhesive should be such that articles to be bonded have limited adhesion initially and can be peeled off without adverse effect; i.e., a piece of paper could be placed on the adhesive and have limited holding strength and yet be peeled off without tearing. PA1 (b) The adhesive and the article to be bonded, once in the proper position, must form a good bond in a short period of time (hours), or a good bond should be formed immediately through the use of pressure. PA1 (c) The adhesive, once the bond has formed, must have resistance to shear under load. PA1 (d) The adhesive should have adequate peel adhesion once the bond is formed. PA1 X is a copolymerizable vinyl group; PA1 Y is a divalent linking group where n.sub.1 can be 0 or 1; and PA1 Z is a monovalent polymer moiety having a general formula ##STR1## wherein R.sup.2 is hydrogen or a lower alkyl group, R.sup.3 is a lower alkyl group, n.sub.2 is an integer from 40 to 500 and R.sup.4 is a monovalent radical selected from the group consisting of ##STR2## and --CO.sub.2 R.sup.6 wherein R.sup.5 is hydrogen or a lower alkyl group and R.sup.6 is a lower alkyl group; which process comprises: PA1 (a) continuously feeding to a wiped surface reactor raw materials which comprise at least one vinyl compound, at least one additional compound as described above, and at least two initiators for free radical polymerization, under the following conditions: PA1 (b) reacting the raw materials to desired conversion; and PA1 (c) continuously withdrawing a polymeric material from the reactor. PA1 R.sup.9 is a single bond on a methylene or ethylene group, the last two of which can have subsitituents comprising an alkyl group having 1 to 6 carbon atoms or a phenyl group; PA1 R.sup.l0 and R.sup.ll are independently hydrogen, an alkyl or cycloalkyl group having 1 to 12 carbon atoms, an aryl or aralkyl group having 6 to 12 carbon atoms, or R.sup.1O and R.sup.ll taken together with the carbon atom to which they are attached to form a 5- to 12-membered carbocyclic ring.
U.S. Pat. No. 4,304,705 describes the preparation of radiation curable polymeric coatings, including coatings made from acrylate polymers, from ethylenically unsaturated azlactone polymers having pendant azlactone groups. These polymers and coatings are said to be useful in imaging systems such as are used in the graphic arts.
Graft copolymers having macromolecular polystyrene side chains and various acrylate backbone polymers are described in U.S. Pat. No. 3,786,116, see especially examples 30-37 which are preparations of such copolymers by solution, suspension and emulsion reactions.